This invention is directed generally to conditioning, e.g., cleaning, the interior surface of hollow containers, and more particularly to conditioning the hollow interior of a bulk container used for the storage of a charge of an ultra-high purity liquified gas by means of a vaporization-condensation reflux action of the liquified gas.
At present a need exists for conditioning transportable or stationary bulk containers, e.g., containers having a capacity in excess of 49 liters, so that they are suitable for storing liquified gas products that meet the moisture, metal contaminant, and particle specifications for ultra high purity (UHP) for high-technology industries. As will be appreciated by those skilled in the art the meaning of the term UHP varies from application to application. For example, in some applications a UHP product is defined as having contaminants at  less than 1 ppm. In other so-called UHP applications the level of contaminants can be higher or lower. While various systems and techniques have been disclosed in the prior art for cleaning small vessels or other small containers, or small parts, such systems and techniques are not suitable for conditioning bulk containers.
For example, some prior art systems, like those to be described later, make use of an exogenous solvent to condition or clean the walls of a container or other part. The use of such solvents is less than desirable for various reasons, one of the most significant being that some solvent may remain as a potential contaminant.
Other systems for cleaning or conditioning containers roll or otherwise agitate the container during the conditioning process. As will be appreciated this approach is impractical and is potentially dangerous for bulk container applications.
The use of condensate reflux for conditioning or cleaning containers or tanks offers various advantages over the above mentioned prior art cleaning techniques. As will be appreciated by those skilled in the art, condensate reflux, in general, is a well known one for various applications. For example, it is known to use vaporization and condensate reflux to purify a liquid sample. Such a method is known universally as distillation and is a common laboratory and industrial procedure for purification of liquids. A laboratory scale apparatus illustrative of this type of prior art is described in Siemer and Brinkley (Analytical Chemistry, 1981, Vol. 53, No. 4, 750-751). This application employs an Erlenmeyer flask with a novel reflux cap to purify a sample of acid. When used in such a way, refluxing acid rinses the walls of the flask continuously and provides the benefits of preventing droplet loss during spattering and providing a safe means of adding other reagents to the flask.
It is also known to use vaporization and reflux as a vehicle to collect product in solution. An apparatus illustrative of this type of prior art is disclosed in U.S. Pat. No. 6,056,929 (Hassal). The apparatus and process disclosed is for the production of radioactive Iodine-125 from the decay of irradiated Xenon-124. The Iodine-125 product coats the vessel used to collect it and a reflux of an aqueous sodium hydroxide solution is used to rinse the product from the walls. Heat is applied at the base of the vessel by immersing the collection vessel in a water bath containing a heater element. This operation vaporizes some of water from the sodium hydroxide solution, which subsequently condenses on all internal walls of the container and dissolves Iodine-125 from the walls before dripping into the pool of sodium hydroxide at the bottom of the vessel. At the end of the reflux procedure, the water bath is replaced with an ice bath to cool the vessel and condense any remaining water vapor into the liquid pool. The liquid product, a sodium hydroxide solution containing Iodine-125, is drained from the collection vessel into a container suitable for storage and delivery.
The use of a condenser and an evaporator coil to produce reflux liquid of a solvent is a well known technique suitable for cleaning metal parts. Such a device is known as a vapor degreaser. U.S. Pat. No. 4,357,212 (Osterman et al.) and Japanese Unexamined Patent Application No. JP95096257A are illustrative of such devices. In such a device, the degreasing solvent is vaporized in a chamber where metal parts are placed. The hot vapor condenses on the metal surfaces, forming a liquid stream that solubilizes grease, oils, and dirt. The liquid drips into the sump and carries with it the contaminants. Any non-condensed vapors are liquefied by a condenser coil at the top of the chamber. In the patent to Osterman et al. the process uses a closed refrigeration cycle with a compressor, vaporizer, condensing coil, and a vapor-liquid separator to generate vapor and reflux of cleaning solvent in the cleaning chamber. The Japanese patent uses a heating coil to generate solvent vapors and a water-cooled condenser to create reflux. While such systems may be suitable for their intended purposes, they necessitate the use of a condenser, which in the case of a bulk storage container would have to be located either internally or externally of the container to produce the liquid reflux condensate.
Another known cleaning application using reflux liquid is washing the surface of immersion heaters installed in waste tanks. An example of such a process is described by Dunn (Battelle-Northwest Lab Report No. BNWL-101, 1965). Immersion heaters are installed inside waste tanks to concentrate contaminants in the liquid phase and an external condenser is used to generate reflux. While this technique may also be suitable for its intended purposes it does not allow the vessel to be used for ultra-high purity product without further cleaning since it uses a waste stream that is completely discarded.
U.S. Pat. No. 2,956,911 (Jalen) discloses a vapor phase and reflux liquid treatment of rubberlike elastomer claddings on vessels to aid in the removal of such claddings from the metal surface. In particular, in this patent a suitable solvent is chosen dependent upon the nature of the elastomer to be removed. The vessel is filled with an amount of solvent that covers a heating element at the base. Heat is applied, which generates solvent vapors. The solvent vapors are condensed and returned to the vessel as reflux; no solvent vapor is purged from the vessel. The combined vapor contact and liquid washing effect breaks the bond between the elastomer cladding and the metal surface of the vessel. After treating the coating with solvent for a suitable period, heat is removed and the vessel is cooled. The solvent is drained from the vessel as a liquid and any residual solvent vapors are removed with steam treatments. The coating is easily removed from the metal surface if it has not already sloughed off in sheets.
U.S. Pat. No. 4,597,768 (Thijssen et al.) discloses a method for concentrating a suspension of solid particles by moving it through a contact zone, wherein the particles are separated from a mixture by crystallization using a cooled heat exchanger prior to being moved through the contact zone.
The present invention relates to process for conditioning a bulk container and a bulk container conditioning system. The bulk container is arranged for storing a charge of an ultra high purity liquified gas and has at least one wall with an interior surface bounding a hollow interior.
The method entails providing a conditioning quantity of the ultra high purity liquified gas into the interior of the container so that a gas space is created above the level of the conditioning quantity of the liquified gas. A temperature difference is imposed on the container to cause the conditioning quantity of the liquified gas to produce vapor in the gas space. The vapor is enabled to condense on the interior surface of the container, without the use of a condenser, whereupon liquid reflux is created. The liquid re flux washes the interior surface of the container, e.g., removes any moisture, impurities, metals, etc. from the interior surface of the container, to condition that surface so that the container is ready to accept for storage a fresh charge of the ultra high purity liquified gas.
In accordance with one aspect of the invention when the ultra-high liquified gas liquifies at a temperature at or above the ambient temperature, the method entails and the system makes use of a heating element for heating the container to impose the temperature difference on the container to produce the vapor for condensation on the interior surface of the container. Moreover, a venting valve is provided to enable a portion of the vapor produced to vent from the gas space. For liquified gases that liquify at a temperature below the ambient temperature the method entails and the system makes use of a venting valve for enabling a portion of the vapor to vent from the interior of the container to cause the portion of the vapor remaining within the gas space to condense on the interior surface of the container to produce the liquid reflux.
In either method the liquid reflux that washes the interior of the container reunites with the conditioning quantity of liquified gas within the container to produce a degraded quantity of the liquified gas in the container for ultimate removal and optional reclamation to produce a quantity of ultra high purity liquified gas suitable for reuse.
In accordance with another aspect of the invention the vapor which is vented from the valve may also be reclaimed to produce a quantity of the ultra high purity liquified gas.